Pluto

Pluto is a small, icy world first discovered in 1939, and recognized as the ninth planet in the Solar System until quite recently. Its orbit was tilted instead of level like the other planets orbiting the Sun. It is now considered a dwarf planet and many astronomers speculate and believe it is not part of the Solar System. To this day, there has been many conflicts whether it was a planet or not. It has one satellite named Charon.

Pluto (冥王星; Star of the Underworld's King) was the ninth planet of the Solar System within the Sailor Moon series. In reality, Pluto was reclassified as a "dwarf planet" in August 2006, leaving only eight classical planets in the Solar System. Before the reclassifying of the planets, Pluto was grouped with Jupiter, Saturn, Uranus, and Neptune as a planet of the outer Solar System. It has three moons, named Charon, Nix, and Hydra, although Charon is currently also classified as the twin planet of Pluto.

Currently, Pluto is one of the least understood objects in the Solar System due to its extreme distance from the Earth. It has a diameter of roughly 2300 km, making it smaller than the Moon by about 33%. Pluto's thin atmosphere is comprised primarily of nitrogen, methane, and carbon monoxide, the same substances that make up its icy surface. The surface temperature is approximately -230 degrees Celsius.

In the Cowboy Bebop universe, Pluto is the site of a maximum security penitentiary, which is fitting considering its desolate environment and remote distance from the other planets. A prison ship destined for Pluto Penitentiary filled with criminals, among them Udai Taxim, malfunctioned in Black Dog Serenade.